Permanent magnet alternating current (PMAC) motor systems may be utilized in many different applications and are well-known in the art. Some PMAC motor systems include a PMAC motor connected to each phase of a three-phase inverter, and a controller connected to the PMAC motor and the three-phase inverter in a configuration known as a three-phase PMAC motor.
The three-phase inverter is configured to provide voltage to the PMAC motor to control the amount of torque produced by the PMAC motor. To do this, each inverter phase is coupled between a voltage source and the PMAC motor, and includes a pair of (e.g., a high-side and a low-side) field effect transistors (“FETs”) or other type of solid state switching devices that, via their switching operations (i.e., ON/OFF functions), control the amount of voltage provided to the PMAC motor. The switching operations of the switching devices are typically controlled using pulse-width-modulation (“PWM”) techniques. Specifically, the switching devices are connected to provide three-phase voltage to the A, B, and C phases of the PMAC motor. During operation, the A, B, and C phases of the PMAC motor are maintained 120 degrees (electrical) apart. For example, if phase A is at 120 degrees (i.e., θ=120°), then phase B would be at phase A plus 120 degrees (i.e., θ+120°), and phase C would be at phase A minus 120 degrees (i.e., θ−120°).
The amount of torque produced by the PMAC motor is functionally related to the amplitude of the electric current in the A, B, and C phases, which is also referred to as the motor current. The frequency of the motor current is selected to create a magnetic field or flux in the phase windings that rotate about an armature at a predetermined speed, which induces a rotor in the PMAC motor to rotate. The rotational speed of the rotor is thus determined by the amplitude and frequency of the motor current.
Typically, the rotating flux is commanded to lead the rotor by some angle, which is often referred to as an “advance angle.” The advance angle can be controlled by adjusting the phase angle of the current supplied to the PMAC motor windings, and is increased as the rotor speed increases, depending on the torque and power requirements of the PMAC motor. If the flux is not leading the rotor by the proper advance angle and/or if the flux does not include the proper rotational speed, the PMAC motor may experience high currents and/or torque oscillations, which can result in damage the PMAC motor system.
To prevent the PMAC motor from experiencing high currents and/or torque oscillations, PMAC motor systems track the present position of the rotor (or the flux) and the present motor speed at all times. As such, PMAC motor systems typically include an absolute position sensor (e.g., a resolver) to synchronize the rotor position and the motor speed, or employ a control algorithm that estimates the rotor position and motor speed without the use of a mechanical sensor, which control algorithm is often referred to as a “sensorless algorithm” or a “sensorless control algorithm,” to track the present position of the rotor (or the flux) and the present motor speed during operation.
A sensorless control algorithm is typically performed by the controller, and the controller estimates the present rotor position and present motor speed based on a measurement of the inverter output voltage (i.e., the voltage in each inverter phase) and the inverter output current (i.e., the current in each inverter phase). In some sensorless control algorithms, the controller assumes that the rotor is at a “zero position” and that the motor has a “zero speed” (i.e., is at rest) when starting (or restarting) the sensorless control algorithm. A problem may arise in this type of sensorless control algorithm because there can be times when the rotor may not be at the “zero position” because the rotor is rotating when the controller starts the sensorless control algorithm. For example, an engine fan rotor may be rotating at the start of the sensorless control algorithm because air flowing through the engine is applying a force to the fan blades, which causes the rotor to rotate, while a motor vehicle is being driven. Similarly, execution of the sensorless control algorithm may be interrupted due to external events (e.g., the PMAC motor system being exposed to strong electromagnetic interference), or by the unlikely event of a diagnostic malfunction, both of which would require that the controller restart the sensorless control algorithm while the PMAC motor is operating and the rotor is rotating. That is, in each of these situations, the sensorless control algorithm has to be started or restarted without any knowledge of the present rotor position and present motor speed (referred to hereinafter as “initial conditions”).
To solve this problem, PMAC motor systems typically use one or more additional circuits and/or sensors to calculate the initial conditions. Specifically, these additional circuits and/or sensors detect the actual output voltage of the inverter and calculate the initial conditions based on the detected inverter output voltage. In these PMAC motor systems, after the sensorless control algorithm is stopped and the controller is reset, the proper initial conditions (i.e., the newly calculated rotor position and motor speed) are calculated based on the measured inverter output voltage, and a restart portion of the sensorless control algorithm is performed in order to provide the proper initial conditions to the sensorless control algorithm.
Accordingly, it is desirable to provide PMAC motor systems and methods for starting or restarting a PMAC motor system sensorless control algorithm without needing additional circuits and/or sensors to detect the inverter output voltage and using the inverter output voltage to calculate the proper initial conditions. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.